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An Early Cretaceous zamiaceous cycad of south west Gondwana: Restrepophyllum nov. gen. from Patagonia, Argentina

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An Early Cretaceous zamiaceous cycad of south west Gondwana: Restrepophyllum nov. gen. from Patagonia, Argentina
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  See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/230801392 An Early Cretaceous zamiaceous cycad of SouthWest Gondwana: Restrepophyllum nov. gen.from Patagonia, Argentina  Article   in  Review of Palaeobotany and Palynology · May 2010 DOI: 10.1016/j.revpalbo.2010.04.001 CITATIONS 17 READS 97 3 authors , including: Some of the authors of this publication are also working on these related projects: Polen and leaves of Early Cretaceous angiosperms from Patagonia. Biostratigraphy   View projectMauro G. Passalia 23   PUBLICATIONS   367   CITATIONS   SEE PROFILE Georgina Del FueyoMuseo Argentino de Ciencias Naturales "Ber… 34   PUBLICATIONS   387   CITATIONS   SEE PROFILE All content following this page was uploaded by Georgina Del Fueyo on 05 January 2017. The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the srcinal documentand are linked to publications on ResearchGate, letting you access and read them immediately.  An Early Cretaceous zamiaceous cycad of South West Gondwana:  Restrepophyllum nov. gen. from Patagonia, Argentina Mauro G. Passalia a, ⁎ , Georgina Del Fueyo b , Sergio Archangelsky b a Instituto de Investigaciones en Biodiversidad y Medioambiente, CONICET-UNCo, S.C. de Bariloche, Argentina b Museo Argentino de Ciencias Naturales  ‘  Bernardino Rivadavia ’  , CONICET. Buenos Aires, Argentina a b s t r a c ta r t i c l e i n f o  Article history: Received 29 October 2009Received in revised form 25 March 2010Accepted 2 April 2010Available online 13 April 2010 Keywords: Cycads Restrepophyllum  nov. gen. Chigua (Zamia) Cuticular ultrastructureAptianArgentina The record of Cycadales in Patagonia begins in the Triassic and extends up to the Oligocene. In this region thegroup is highly diversi fi ed and includes several taxa represented by trunks, leaves and pollen cones. A newcycadalean genus and species,  Restrepophyllum chiguoides , form the Aptian An fi teatro de Ticó Formation,Santa Cruz province, Argentina, is described here. The fossil is a leaf compression with well-preserved cuticle.Its morphology, anatomy and ultrastructure are studied by means of light and electron microscopy. The leaf is lanceolate, serrate, and possesses a prominent midvein and decurrent laterals showing an open, simple ordichotomous venation. The leaf is hypostomatic, and the abaxial cuticle is thinner than the adaxial one. Thestomata are irregularly distributed and indistinctly oriented between veins. They are monocyclic toimperfectly dicyclic (haplocheilic); the suprastomatal aperture is raised over the epidermis and the guardcells are sunken. Scattered trichomes and crystalliferous idioblasts are also present. The cuticle is composedof three layers: the outer and inner layers are lamellate, while the middle one is granulate. This new cycadleaf is compared with similar fossil leaves from Gondwana and Europe/North America, and also with similarextant cycad leaves. Based on the general morphology and the main characters of the cuticle,  R. chiguoides  isassigned to the family Zamiaceae; moreover it is more closely related to the living  Zamia  ( Chigua )  restrepoi (D. Stevenson) Lindstrom than to any other member of the Cycadales. Paleophytogeographic evidencesuggests a South American srcin of   Zamia/Chigua  and a further migration to northern latitudes. This newtype of leaf also suggests the putative existence of a  Chigua  clade that may be traced back to the EarlyCretaceous when two cycadalean families, Zamiaceae and Stangeriaceae, were already well-established inPatagonia.© 2010 Elsevier B.V. All rights reserved. 1. Introduction The Cycadales represent an ancient lineage of plants that once fl ourished and diversi fi ed, thus successfully attaining a worldwidedistribution. The fossil record of this group begins in the Carboniferousand reaches its acme during the Mesozoic, when the three recognizedextant families, Cycadaceae, Zamiaceae and Stangeriaceae  —  amongother extinct cycads  —  appear to have already srcinated (Taylor et al.,2009).Cycadsarerestrictedtodaytotropicalandsubtropicalclimatesof both South and North Hemispheres and have widely disjunctdistribution (Stevenson 1990, 1992). Within Southwestern Gondwana, Antarctica and Patagonia yield aremarkable richness of macrofossil remains mostly assigned to theZamiaceae.Hermsen et al. (2006, 2007, 2009) studied permineralized material from the Triassic of Antarctica: stems of   Antarcticycas , leavesof   Yelchophyllum  and pollen cones of   Delemaya  co-occurring in thesame beds. They presented a reconstruction of a whole-plant thatlookslikea small  Zamia Linnaeus. Cetricycas  Cantrill,a permineralizedstem assigned to the subfamily Encephalartoideae of the Zamiaceae,has been found in the Late Cretaceous of the Antarctic Peninsula(Cantrill, 2000). Impression of   Nilssonia  Brongniart and  Pseudoctenis Seward leaf remains attributed to the extinct family Nilssoniaceaehave also been described from the late Jurassic/early Cretaceous of Antarctica by Gee (1989).In Patagonia, the oldest cycadalean remains occur in the Triassicand they persist up to the Oligocene. Fossils are represented by bothvegetative (stems and leaves) and reproductive organs (pollencones). The oldest known cycad in Argentina is the silici fi ed stem of  Michelilloa  Archangelsky and Brett from the Upper Triassic Ischigual-asto Formation that was related to the extant genus  Dioon  Lindley of the Zamiaceae based on the structure of the leaf gap and long fi lamentous hairs found in the stem epidermis (Archangelsky andBrett, 1963) .  Other petri fi ed stems were found in Patagonia in theUpper Cretaceous Allen Formation:  Brunoa  Artabe, Zamuner andStevenson,  Worsdellia  Artabe, Zamuner and Stevenson and  Chamber-lania  Artabe, Zamuner and Stevenson.  Brunoa  and  Worsdellia  were Review of Palaeobotany and Palynology 161 (2010) 137 – 150 ⁎  Corresponding author. Tel./fax: +54 2944 433040. E-mail addresses:  passaliam@gmail.com (M.G. Passalia), georgidf@yahoo.com.ar(G. Del Fueyo), sarcang@ fi bertel.com.ar (S. Archangelsky).0034-6667/$  –  see front matter © 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.revpalbo.2010.04.001 Contents lists available at ScienceDirect Review of Palaeobotany and Palynology  journal homepage: www.elsevier.com/locate/revpalbo  assigned to the Tribe Diooeae and  Chamberlania  to Tribe Encepha-larteaeoftheEncephalartoideae(Artabeetal.,2004,2005).Moreover,two petri fi ed stems i.e.  Bororoa  Petriella (related to the extant Macrozamia  Miquel of the Encephalarteae) and  Menucoa  Petriella(relatedtotheCycadaceaebutalsototheZamiaceae – Encephalarteae)were described from the Paleogene of Patagonia (Petriella, 1969,1972).Pollenconesofthree  Androstrobus Schimperspecies(  Androstrobusmunku ,  Androstrobus patagonicus  and  Androstrobus rayen ) found inthe Aptian An fi teatro de Ticó Formation of Santa Cruz province, havebeen described with  in situ  pollen grains which show an af  fi nity toeither the Zamiaceae or Cycadaceae (Archangelsky and Villar deSeoane, 2004).Cycadalean fossil leaf remains from Patagonia are mostly based onimpressions. They are more abundant and diverse than stems andpollen cones and have an uninterrupted record that begins in theTriassic (Artabe, 1985) and continues throughout the Jurassic (Artabe et al., 1991), andCretaceous(Archangelsky, 1997) to their last known occurrence in the Oligocene (Berry, 1938). However, other fossil leaves have been assigned to the Cycadalesbased on their distinctive cuticular features (stomata and epidermalcells). They were recovered in the early Cretaceous sediments of theBaqueró Group in Patagonia. The genera  Mesosingeria  Archangelsky, Mesodescolea  Archangelsky and  Sueria  Menéndez, are considered tobe endemic to Patagonia (Archangelsky, 2003).  Mesodescolea plicata Archangelsky was found to be related to the extant  Stangeria  Moore(Artabe and Archangelsky, 1971) while  Mesosingeria parva  Villar deSeoane may be related to  Encephalartos  Lehmann (Villar de Seoane,1997) and  Sueria rectinervis  Menéndez to  Zamia  and  Ceratozamia Brongniart (Artabe, 1994). One particular locality, Bajo Grande inSanta Cruz province, yielded several cutinized leaf remains of cycadaleans:  Almargemia incrassata  and  Ticoa lamellata  (Archan-gelsky, 1966),  Pseudoctenis dentata  and  Pseudoctenis crassa  (Arch-angelsky and Baldoni, 1972),  Sueria elegans  and  Mesosingeria parva (Villar de Seoane, 1997) and  Mesosingeria oblonga  (Villar de Seoane,2005). It is interesting to note that the three  Androstrobus  speciesoccur at the same locality (Archangelsky and Villar de Seoane, 2004).In this paper we describe a new cycadalean genus based on a leaf compression recovered from the An fi teatro de Ticó Formation at theBajo Grande locality. The morphology, anatomy and ultrastructure of the lea fl et are described using light and electron (scanning andtransmission) microscopy. The general morphology and cuticlestructure suggest that the lea fl et can be assigned to the familyZamiaceae, and that is probably closely related to extant  Zamia ( Chigua )  restrepoi  (Stevenson) Lindstrom. Restrepophyllum  further underlines the variety that Cycadalesattained in the Ticó Flora (i.e., all assemblages that are found in theAn fi teatro de Ticó Formation at several localities, including BajoGrande) and demonstrates once more the relevance of this group inPatagonian plant communities during the early Cretaceous. 2. Material and methods The fossil consists of a single incomplete lea fl et compression(apical tip and base missing) with cuticle preserved. The specimenwascollectedbyM.LlorensandG.CladeraattheEstanciaBajoGrandelocality in Santa Cruz province, Argentina, during a  fi eld trip insummer 2002 (see location map and stratigraphic section in Claderaet al., 2007). The fossil came from sediments belonging to the earlyLateAptianAn fi teatrodeTicóFormation,thebasalunitoftheBaqueróGroup (Cladera et al., 2002).Thelea fl etcuticlewasremovedfromthematrixandoxidizedin40%nitric acid during 5 – 10 min, followed by 5% ammonium hydroxideduring2 min.Also,alea fl etfragment,counterpartofBAPb12872b,wasmacerated in 20% hydrochloric acid followed by 70% hydro fl uoric acidyielding several cuticle fragments. Some cuticles showed carbonizedresidues that were removed with 50% sodium hypochlorite. A middlefragment of a dried herbarium lea fl et of   Zamia  ( Chigua )  restrepoi (Stevenson) Lindstrom was cut into small sections, less than 3 mm 2 ,withbothadaxialandabaxialepidermisandrehydrated.Toexaminetheepidermis of inner surfaces, some of these sections were gentlymacerated, for less than 45min, in 20% chromium trioxide solutionfollowing Alvin and Boulter (1974). Cleared lea fl ets of   Zamia  ( Chigua ) restrepoi  (Stevenson) were also obtained for study.For light microscopy (LM) observation, fossil cuticles andepidermis of   Zamia  ( Chigua )  restrepoi  were stained with safranin,mountedinglycerinejellyandobservedwithaLeitzDiaplanandZeissAxioscope 2 microscopes. Light micrographs were taken with a LeicaDFC 280 and a Nikon Coolpix 990. For scanning electron microscopy(SEM), fossil cuticles were mounted on exposed  fi lm and extantepidermis on double-sided adhesive tape, both attached to stubs andcoated with gold. Observations were made under a SEM Jeol-T 100 at15.1 KVatLaPlataNaturalHistoryMuseum.Fortransmissionelectronmicroscopy (TEM), selected fragments of   Restrepophyllum chiguoides cuticleandof   Zamia ( Chigua ) restrepoi epidermisthatwerepreviously fi xed in glutaraldehyde were both stained with 2% osmium tetroxidefor 2 h at room temperature. The material was then rinsed in distilledwateranddehydratedinanalcoholseries,in fi ltratedwithSpurrresin,placed in moulds and dried in vacuum at 70 °C. Finally, ultrathinsections (ca. 800 Å thick) were made with a diamond knife using aSorval automatic, mounted in single hole grids coated with Formvarand stained with lead citrate (1 ′ ) and uranyl acetate (10 ′ ). Observa-tions were made with a Jeol JEM 100C at 85.0 kV at the ElectronicMicroscopy Laboratory of CICV-INTA Castelar.The fossil specimen, microscope slides and samples for SEM andTEM are deposited in the paleobotanical collection of the MuseoArgentino de Ciencias Naturales Bernardino Rivadavia under thepre fi xesBAPb,BAPbPm,BAPbMEBandBAPbMET.Theextantstudiedmaterial are deposited as BAPb Pm 585 – 587, BAPb MEB 336, 337, andBAPb MET 230 – 232. Number of samples observed as well as resinblocks and cupper grids made are as follow: for BA PB Pm 563, 570,571, 575, 576, 580, 585, 586 and 587 one sample each; for BA PB Pm564,565,569,573,574,577,578and579twosampleseach;forBAPBPm 562, 572 and 581 three samples each; for BA PB MEB 339 onesample; for BA PB MEB 336 and 337 two samples each; for BA PB MEB335and338threesampleseach;forBAPBMEB fi vesamples;forresinblock BA PB TEM 230, 35 samples and 15 cupper grids; for resin blockBA PB TEM231, 25 samplesand 12cupper grids;for resin block BA PBTEM232,5samplesand4cuppergrids;forresinblockBAPBTEM233,5 samples and 4 cupper grids and for resin block BA PB TEM 234, 25samples and 12 cupper grids.The terminology for the cuticular membranes description followsHolloway (1982). 3. Systematic descriptions Order Cycadales P fi tzerFamily Zamiaceae Reichenbach Restrepophyllum  nov. gen.Type species:  Restrepophyllum chiguoides  nov. sp. Etymology : the generic epithet refers to the close similarity of thislea fl et with the living species  Zamia  ( Chigua) restrepoi , which wasdedicatedto the ColombianbotanistsPadre Sergio Restrepo Jaramillo. Diagnosis : Leaf (lea fl et?) papyraceous, narrow, lanceolate with serratemargins and simple, regularly spaced teeth. Open venation with aprominent midvein and decurrent laterals at acute angles, reachingmargins,simpleordichotomous.Leafhypostomatic.Abaxialcuticlethinwith isodiametric to elongate epidermal cells between veins andstrongly elongate cells on veins. Stomata present betweenveins, irregularly distributed and indistinctly oriented, mostly 138  M.G. Passalia et al. / Review of Palaeobotany and Palynology 161 (2010) 137  – 150  monocyclic to imperfectly dicyclic (haplocheilic). Suprastomatal aper-ture raised over epidermal surface. Guard cells sunken in epistomatalchamber. Adaxial cuticle thicker with elongate epidermal cells. Comments :  Restrepophyllum  is referred here to the cycads because of its close resemblance to lea fl ets of extant genus  Zamia  ( Chigua ) restrepoi  (family Zamiaceae, Stevenson, 1990) now restricted toColombia, with which it also shares epidermal similarities, especiallyin the structure of stomata. Lea fl ets of   Zamia  ( Chigua )  restrepoi  aresimilarinshapetothoseofotherextantcycadssuchas  Zamia spp.and Bowenia HookerexHooker(i.e. Boweniaserrulata (Bull)Chamberlain)butdifferinhavingamidvein.Othercycads( Cycas and Stangeria )alsopossess lea fl ets with a midvein, but however differ from  Chigua  intheir venation patterns (Stevenson et al., 1996). Restrepophyllum chiguoides  nov. sp.Plates I, II and IV . Fig. 1 Holotype : BAPb 12872; BAPb Pm 562 – 565, 569 – 581; BAPb MEB 334,335, 338, 339; BAPb MET 233 – 234 (all these preparations named asBAPB Pm, BAPB MEB and BAPb MET belong to the single specimenBAPb 12872). Plate I. Restrepophyllum chiguoides  nov.gen. etsp. Figs. 3 – 5were taken with atransmitted-light microscope. Figs. 1 – 2, BAPb 12872 holotype. Figs. 3 – 4, BAPbPm 563 holotype. Fig.5,BAPbPm 564 holotype.1. General aspect of lea fl et. Scale bar=0,5 cm.2. Detail of dentate margin. Obscure line along the margin is produced by the compression border where the cuticle is thicker (arrowheads). Scale bar=0,1 cm.3. Detail of two neighbor stomata with subsidiary cells (sc) in contact. Arrows indicate the stomatal pore. Scale bar=50 µm.4. Detail of stomata showed in  fi gure 3. Arrows indicate the guard cells. Scale bar= 20 µm.5. Detail of crystalliferous idioblasts (arrows). Scale bar=50 µm.139 M.G. Passalia et al. / Review of Palaeobotany and Palynology 161 (2010) 137  – 150  Repository : Museo Argentino de Ciencias. Naturales  ‘ BernardinoRivadavia ’ , División Paleobotánica.Type locality: Estancia Bajo Grande, Santa Cruz province, Argentina. Stratigraphic horizon : Bajo Grande Section, upper plant horizon,Baqueró Group, An fi teatro de Ticó Formation, Aptian. Etymology : The species epithet refers to the close similarity with theliving species  Zamia  ( Chigua) restrepoi.Diagnosis : Lea fl et papyraceous, narrow, lanceolate, slightly falcate,elongate, with a length/width ratio not less than 5:1. Margins serratewith simple regularly spaced teeth. Teeth straight to slightly  fl exuousat base, gently concave to straight apically, with an acute apex androunded sinus. Venation open with a prominent midvein thatgradually diminishes in width towards apex. Lateral veins decurrentat an acute angle, straight to slightly curved, parallel and reachingmargins without anastomizing. At margins, up to two veins percentimeter are present. Veins may remain simple before reachingmargins, or they may dichotomize once at an acute angle halfwaybetween midvein and margin. Cuticle thin, bearing stomata onepidermis on one side of the leaf (hypostomatic), presumablyabaxially. Epidermal cells between veins isodiametric to elongate,with few scattered hairs. Anticlinal walls thin, straight to slightlysinuous, occasionally pitted. Periclinal walls smooth. Epidermal cellson veins rectangular, elongate, forming parallel bands. Stomatairregularly distributed and indistinctly oriented, rarely with subsid-iary cells in contact. Stomatal apparatus with circular to slightly ovaloutline, mostly monocyclic to imperfectly dicyclic (haplocheilic) with5 – 8 subsidiary cells. Suprastomatal aperture circular to oval, typicallyraised over epidermal surface. Guard cells sunken in an epistomatalchamber, thickened around aperture. Description :Onlyonefragmentaryleaf(lea fl et?)lackingits baseandabriefapicalsectorhasbeenfound(PlateI,1 – 2;Fig.1).Theleafappearsto be papyraceous; it is narrow and lanceolate, slightly falcate, 6.8 cmlong(incomplete)and1.3 cmofmaximumwidth(length – widthrationolessthan5:1).Theleafmarginisserrate.Theteetharesimple,withacute apical tips and they are regularly spaced (1.8 teeth per cm).Basal sides of teeth are straight to slightly  fl exuous, while their apicalsides are straight to gently concave. The open venation shows aprominentmidvein,0.8 mmwideatbase,whichgraduallydiminishestowards the apex. Lateral veins are decurrent, at 10° – 20° angles,straight to slightly curved, parallel, without anastomoses, and reachthe margin with angles up to 30°. At the margins there are about 3veins per cm, each up to 0.3 mm thick. Veins may be simple reachingthe apical tips of teeth, or they may dichotomize once at an acuteangle halfway between midrib and margin. In this case the apicalbranch persists to the apical tip of tooth while the lower may reachthe base of the same tooth or the apex of a neighboring tooth.Therefore, each tooth may receive one or two vascular bundles. Theleaf margin exhibits a typical compression border where the cuticle isthicker (Plate I, 2). Except for a small fragment, only one cuticle typewasrecoveredfromtheleafcompressionandthesurroundingmatrix.Thismaterialshowssignsofseveredegradationwithmanyholeswithvery thin and corroded periclinal cell walls and translucent anticlinalcell walls (Plate II, 2, 11 – 13). The epidermal cells between veins areisodiametric to elongate, tetragonal to polygonal, with a maximallengthofabout75 µm(PlateII,2,7 – 9).Anticlinalwallsareabout5 µmthick, straight to slightly sinuous, occasionally pitted (Plate II, 7 – 10).Periclinal walls have a smooth surface. Few scattered hairs arepresents (Plate II, 1, 6). Idioblast containing probably crystals issporadically present among epidermal cells (Plate I, 5). Epidermalcells on veins are clearly differentiated and forming long parallelbands; the cells are rectangular, thin and typically elongate, up to 75 – 100 µm long×15 – 20 µm wide (Plate II, 13). They show no stomata,hairs or papillae. Common epidermal cells gradually become elongatewhen approaching the bands of long cells that characterize the veins(PlateII,2).Thestomataareseenasdistinctstructuresthatareclearlyvisible in the cuticle, and often they are partly broken away from thesurrounding epidermal cells, leaving large empty spaces. They areirregularly distributed and indistinctly oriented, 24 per mm 2 , andsporadically have subsidiary cells in contact (PlateI, 3; Plate II, 9). The stomatal apparatus is circular to slightly oval in outline; it is mostlymonocyclic to imperfectly dicyclic (haplocheilic), with 5 – 8 subsidiarycells in external cycle. Subsidiary cells are not strictly differentiatedinto polar or lateral and rather similar in appearance to the commonepidermal cells (Plate I, 3 – 4; Plate II, 7 – 12). However, some stomatalapparatus show elongate subsidiary cells in polar position (Plate II, 7,9, 11). The suprastomatal aperture is circular to oval, 20 – 35 µm, andraised over the epidermal surface, forming a characteristic solid ringas a bell-like structure that protects the spherical and slightly sunkenepistomatal chamber (Plate II, 3 – 5). This elevated structure showscharacteristic thin concentric rings (Plate II, 4). Guard cells are oftenseenpartiallypreservedandsunkenintheepistomatalchamber;theyare elongate and thickened around the aperture (Plate II, 10 – 12). Asmall fragment of a second (presumably adaxial) cuticle was foundadhered to the  fi rst section of cuticle: it shows no stomata and onlyelongate rectangular cells.With TEM, epidermal cells in transverse section show periclinalwalls of variable thickness according to their disposition along thelea fl ets; marginal cells are thicker than those of the blade (Plate IV ,1 – 3). In the teeth, the adaxial cuticle has an average thickness of 3.5 µm(3 – 4.6 µm) whiletheabaxialonehave an average thicknessof 1 µm (0.8 – 1.6 µm) (Plate IV , 1 – 2). In the lea fl et blade, both upper andlower cuticles also show different thickness, the former with anaverage of 1 µm (0.6 – 1.2 µm) and the latter 0.6 µm (0.5 – 0.7 µm)(PlateIV ,3).Duetocompressionandpoorpreservation,insomeareasof the blade, the adaxial and abaxial cuticles both measure 0.5 µmthick, while in other regions they are 0.8 µm thick. Carbonizedmesophyll is preserved between the two blade cuticles (Plate IV , 3).At ultrastructural level the cuticle on the leaf margin has a betterpreservationthan the lamina.Periclinal wallsin teeth have twolayersof the cuticular membrane and the remains of what is assumed, thecellwall.Theouterlayer,thecuticleproperorsublayerA1inthesenseof  Archangelsky et al (1986), is lamellate of 0.06 µm thick in theadaxial cuticle and 0.02 µm thick in the abaxial cuticle, with up to 4lamellae that run almost parallel to the surface (Plate IV , 5 – 6).Remains of extracuticular material probably belonged to epicuticularwaxes may occur on the external surface as an amorphous more Plate II.  Restrepophyllum chiguoides  nov. gen. et sp., scanning electron micrographs of lea fl et abaxial cuticle. Figs. 1, 3, 4, 6, BAPb MEB 334 holotype. Figs. 2, 8, 11, 12, BAPb MEB 335holotype. Figs. 5, 7, 9, 10, 13, BAPb MEB 339 holotype.1. Outer view of cuticle showing, isodiametric epidermal cells and stomata randomly disposed. Arrowhead indicates a trichome. Scale bar=100 µm.2. Inner view of cuticle, showing the transition zone of epidermal cells, longer and narrower on the veins (top), to isodiametric-polygonal in the stomatiferous area(bottom). Scale bar=100 µm.3 – 5. Outer views of stomata showing circular to oval suprastomatal apertures raising over the epidermal surface. Note thin concentric cuticular rings (arrowheads) andremains of guard cells (arrows). Scale bar=10 µm.6. Outer view of cuticle, showing a detail of the trichome appointed in Fig. 1. Note distal part broken. Scale bar=10 µm.7 – 12. Inner views of stomata illustrating the variability in the number and disposition of the subsidiary cells (sc). Note the elongate polar subsidiary cells (arrowheads) in fi gures 7, 9 and 11 (in the last one the polar subsidiary cell of the right is transversally divided). Arrows in  fi gures 9 – 11 show remains of guard cells. 7 – 9, 12, scalebar=50 µm. 10, scale bar=10 µm. 11, scale bar=20 µm.13. Inner view of cuticle, showing elongate epidermal cells on the veins. Note the deep anticlinal walls more or less damaged. Scale bar=50 µm.140  M.G. Passalia et al. / Review of Palaeobotany and Palynology 161 (2010) 137  – 150
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